High folic acid in pregnancy could cause early bleeding

Women taking high-dose folic acid supplements during early pregnancy may face an increased risk of vaginal bleeding, according to new research led by Flinders University. The study, published in the journal Reproductive Health, raises important questions about supplementation levels in countries with mandatory folic acid food fortification.

Vaginal bleeding affects around one in five pregnancies and can be a distressing experience for expectant parents. While it does not always signal a serious problem, it has previously been linked with an increased risk of pregnancy complications.

The research compared two Adelaide pregnancy cohorts, totalling more than 2400 first-time mothers, recruited before and after Australia introduced mandatory folic acid fortification of bread-making flour in September 2009. Women recruited after fortification were much more likely to be taking high-dose supplements and had higher folate levels overall.

The team found that women taking at least 800 micrograms of folic acid daily were more likely to report spotting and mild bleeding during the first 16 weeks of pregnancy. In pregnancies carrying a boy, the risk of vaginal bleeding was more than double compared with women who did not take folic acid supplements.

Senior author Professor Claire Roberts said the findings point to a previously unrecognised interaction between folic acid intake, the sex of the baby and pregnancy health.

“This is the first study to show that the relationship between folic acid supplementation and vaginal bleeding appears to differ depending on whether a woman is carrying a boy or girl,” Roberts said.

“We also found that vaginal bleeding in early pregnancy is associated with later complications including spontaneous preterm birth, placental abruption and shorter gestation.”

The study found that male-bearing pregnancies appeared particularly vulnerable. Among women who experienced vaginal bleeding, those carrying boys were more likely to give birth earlier than women who did not experience bleeding.

The researchers said the results do not challenge the well-established benefits of folic acid — a form of the B vitamin folate — in preventing serious birth defects, with lead author Dr Hongyan Wang noting that folic acid remains a critical nutrient before and during early pregnancy.

The findings do however underscore the need for more research into what constitutes the safest and most effective upper limit of folic acid intake during pregnancy, particularly in an era where many women already receive folic acid through fortified foods. Indeed, only a year ago Flinders University researchers linked Australia’s rising incidence of gestational diabetes mellitus in part to excess maternal folate levels, due to the dual impact of folic acid in food fortification and higher-than-recommended supplementation doses during pregnancy.

“Our findings suggest that the recommended daily dose of around 400 micrograms may be sufficient for most women in countries where food is already fortified with folic acid,” Roberts said.

“We need further research to understand the biological mechanisms behind these associations and to determine whether supplementation guidelines should be refined.”

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